Balloon angioplasty has been utilized for a number of years to treat coronary arteries narrowed by plaque deposits. A catheter having an inflatable balloon secured to its distal end is advanced through an artery to a narrowed region. The balloon is then inflated with a fluid from an external source, causing the narrowed region of the artery to be expanded. The balloon is then deflated and withdrawn. A serious problem associated with balloon angioplasty has been the occurrence in up to 30% of the cases of so-called restenosis, either immediately after the procedure or within about six months. Immediate restenosis, also known as abrupt reclosure, results from flaps or segments of plaque and plaque-ridden tissue which are formed during balloon angioplasty and which can block the artery. Such blockage of the artery requires emergency surgery and often results in death. Furthermore, a surgical team is required to stand by during the balloon angioplasty procedure. Restenosis at a later time results from causes that are not totally known. Thrombus formation is believed to play an important part. Often repeat balloon angioplasty or surgery is required, and another episode of restenosis may occur.
A technique which has shown great promise for overcoming the problem of restenosis is the simultaneous application of heat and pressure to a plaque-narrowed region of an artery. The technique is described by John F. Hiehle, Jr. et al in "Nd-YAG Laser Fusion of Human Atheromatous Plaque-Arterial Wall Separations in Vitro," American Journal of Cardiology, Vol. 56, Dec. 1, 1985, pp. 953-957. In accordance with this technique, a catheter having an inflatable balloon at its distal end is advanced to a narrowed region of an artery and the balloon is inflated, as in the case of balloon angioplasty. However, in distinction to balloon angioplasty, sufficient heat is applied through the wall of the balloon to fuse the surrounding tissue and thereby eliminate the flaps which can later block the artery. One advantageous means of heating the surrounding tissue is by directing laser radiation through an optical fiber carried by the catheter and terminating within the balloon. The laser radiation is then directed through the balloon wall to cause heating of the surrounding tissue.
Although the laser balloon catheter has been proposed in principle, there are numerous problems and difficulties in constructing a practical catheter suitable for human use. The balloon containing the device for diffusing laser radiation and the deflated catheter containing the optical fiber must be extremely flexible and small in diameter (on the order of 1.0 to 1.5 millimeters) in order to permit navigation of the catheter through an artery to the desired site. The laser balloon catheter is preferably compatible with a guide wire which is used to guide the catheter through the artery to the desired location. Where the guide wire passes through the balloon, shadowing of the laser radiation pattern by the guide wire must be avoided.
Another critical factor is the technique used for heating the surrounding tissue and the associated power level. It has been found desirable to apply radiation which penetrates the surrounding plaque and plaque-ridden tissue and the artery wall and heats that region by radiant heating, in distinction to conductive heating by the balloon. Furthermore, it has been found desirable to apply such radiation at a power level on the order of 30-40 watts for times of on the order of thirty seconds. With such high power levels, it is extremely critical to efficiently transfer the input laser radiation through the fluid which inflates the balloon and through the balloon wall with minimum heat dissipation within the balloon.
Other techniques involving the application of heat in a coronary artery include the so-called "hot tip" as disclosed in U.S. Pat. No. 4,646,737 issued Mar. 3, 1987 to Hussein et al and U.S. Pat. No. 4,662,368 issued May 5, 1987 to Hussein et al, wherein a thermally conductive tip located at the end of a catheter is heated by laser radiation and conducts heat to the surrounding region as it is pushed through a narrowed artery. The hot tip reaches temperatures on the order of several hundred degrees Celsius in order to produce the necessary conductive heating as it is pushed through the artery. The hot tip is unable to expand the artery beyond the conductive tip diameter, which must be limited for passage through the artery. Another heating technique wherein a microwave-radiating antenna is located within an inflatable balloon is disclosed in U.S. Pat. No. 4,643,186 issued Feb. 17, 1987 to Rosen et al. A coaxial transmission line is carried through a catheter and connects to the antenna.
An endoscopic device wherein low power, narrow beam laser radiation is directed through a balloon wall is disclosed in U.S. Pat. No. 4,470,407 issued Sept. 11, 1984 to Hussein. The problem of providing relatively uniform heating of tissue surrounding a balloon at high power levels and without shadowing is not addressed by the Hussein patent.
Prior art techniques have been disclosed for directing laser radiation outwardly from the tip of an optical fiber. A tapered optical fiber surrounded with a diffusing medium for laser radiation treatment of tumors is disclosed in U.K. Patent Application No. 2,154,761 published Sept. 11, 1985. An optical fiber surrounded with a scattering medium for producing a cylindrical pattern of light at the tip of an optical fiber is disclosed in U.S. Pat. No. 4,660,925 issued Apr. 28, 1987 to McCaughan, Jr. A technique for roughening the surface of an optical fiber tip to cause wide angle radiation of laser energy is disclosed by H. Fujii et al, "Light Scattering Properties of A Rough-ended Optical Fiber," Optics and Laser Technology, February 1984, pp. 40-44. None of the prior art techniques provide the combination of small diameter, flexibility, power handling capability and compatibility with a guide wire necessary for a laser balloon catheter.
It is a general object of the present invention to provide an improved laser balloon catheter.
It is a further object of the present invention to provide a laser balloon catheter suitable for use in coronary angioplasty.
It is another object of the present invention to provide a laser balloon catheter capable of delivering and surviving a high power output.
It is another object of the present invention to provide a laser balloon catheter which can be utilized with a guide wire for advancing the catheter through an artery.
It is another object of the present invention to provide a laser balloon catheter which produces substantially uniform heating of tissue surrounding the balloon.
It is still another object of the present invention to provide a method for manufacturing a laser balloon catheter.
It is yet another object of the present invention to provide a laser balloon catheter which is small in diameter and flexible so that it is easily advanced through an artery.
It is yet another object of the present invention to provide a laser balloon catheter wherein heat dissipation of laser radiation within the balloon is limited to allow heating deep into an artery wall without excessive total energy.
It is a further object of the present invention to provide a laser balloon catheter wherein a relatively high proportion of the input laser radiation is delivered through the balloon wall to the surrounding tissue.